Suspended airbridges are generally used in semiconductor devices, such as monolithic microwave integrated circuits (MMICs), in order to isolate and reduce parasitic capacitance between conductors, such as gate, source and drain electrodes. Gallium arsenide (GaAs) semiconductor devices, in particular, may include airbridges formed of conductive material applied by electro-deposition or electroplating techniques, such as plated gold (Au). For example, the airbridges may extend from pad areas to various components of the semiconductor devices. The airbridges are typically covered by an insulating layer, such as silicon nitride (SiNx), for isolating and protecting the semiconductor devices from environmental conditions, such as temperature, moisture, debris, and the like.
Conventional fabrication techniques include applying an adhesion layer to the plated conductive material of an airbridge prior to application of the insulating layer. Generally, the adhesion layer applied to the plated conductive material can be applied by a variety of techniques, such as evaporation. Conductive adhesion materials are typically patterned using lithography and either etch or lift-off processes, which require corresponding processing steps. Also, insulating adhesion layer materials provide generally poor adhesion characteristics, often resulting in delamination (e.g., nitride delamination) of the insulating layer from the airbridge. Such delamination increases the risk of operational failures and raises field reliability issues, as well as increases in-line and assembly scrap.